Merc 9.9 problems

I have a brand new Mercury 9.9 4 stroke which won't run consistently, and the dealer doesn't have a clue.

It will start and run when cold just fine. After running for a while (30 minutes?), it will refuse to start. It may start by depressing the "Throttle only" button and starting at half or more throttle, but then it won't idle. Gas is fresh. I suspect the new-to-me gismo in the fuel line, which I think serves to vent excessive pressure in the tank... not sure. But if it's defective, might it cause problems? What else might be suspect?

Brand new - won't run properly - dealer can figure out the issue = swap for another motor, yelling and stomping your feet until you get one.

I would not tolerate a brand new motor that they are going to fart around with until it's out of warranty and has spent over half it's life in the shop of sitting unused.

Let Merc figure out what is wrong with it while you enjoy a new "perfectly running" motor.

Most jurisdictions have "lemon laws" - see if something applies and don't take no for an answer.

Have a new 9.9 , it will run a couple of days fine then all of a sudden and when I come off plane it quits running , when trying to restart it wont fire and acts flooded but no spark . The most recent diagnosis is that is was overfilled w/oil . Could this shut down the motor because of built up pressure ? New motor , fresh non eth fuel and new valve in fuel line . They say they now have the correct oil level and it runs fine . Could overfilling the oil cause a shutdown?